1. Field of the Invention
This invention relates to a single silicon crystal having low OSF density induced by oxidation and to a method for the production of the single silicon crystal.
2. Description of the Prior Art
Heretofore, various methods have been introduced to the art concerning the growth of single silicon crystals for use in the manufacture of devices of IC, LSI, etc. Among other known methods, the Czochvalski method which effects growth of a single crystal rod by inserting a seed crystal into molten silicon held in a quartz crucible and lifting the seed crystal while rotating it has been finding extensive utility in commercial production of single crystals of silicon (1) because the silicon wafer produced by this method (hereinafter referred to as "CZ wafer") is not readily warped even after it has been subjected repeatedly to a heat treatment and (2) because the CZ wafer produces an intrinsic gettering action and, therefore, defies the otherwise inevitable pollution with heavy metal originating in a process for producing the devices. These two features of the CZ wafer are both ascribable to the oxygen contained in the crystal. In the meantime, this oxygen is a cause for the stacking fault inducible by a heat treatment. When the stacking fault occurs in the active region of a device, it seriously deteriorates the characteristic properties of the device. Efforts have been made, therefore, in search of a method for alleviating the stacking fault. Particularly, the oxidation-induced stacking fault which occurs during the process of oxidation (hereinafter referred to as "OSF") is a very serious problem because heat treatment with oxidation is essential to the process for LSI production. To the device-quality single silicon crystals, the characteristic of sparing susceptibility to the OSF is indispensable. It is widely known that the OSF generating behavior of the single silicon crystal produced by the Czochvalski method (hereinafter referred to as "CZ single silicon crystal") is affected by the condition of crystal growth. The production of a single silicon crystal sparingly susceptible to OSF has been heretofore attained by setting the crystal pulling speed at a level exceeding about 1.3 mm/min (Kinji Hoshi et al, "Nikkei Microdevices, July 1986 issue," pp 87-108).
In recent years, the trend of devices toward scaling down has come to impose an exacting demand on further uniformalization of the dopant concentration distribution in the CZ wafer (which is in proportion to the reciprocal of resistivity). When the single silicon crystal is pulled at such a speed as mentioned above, the uniformity of the dopant concentration distribution cannot be called fully satisfactory as evinced by the test results obtained by the present inventors and shown in Table 3. This statement holds good with the oxygen concentration in the solid solution. When the scaling down of the device's size has advanced further in the future, the demand imposed on the uniformalization is believed to gain all the more in exactitude. Generally, when the crystal pulling speed is high, the uniformity of the dopant and that of oxygen in solid solution tend to dwindle. Thus, the conventional technique has entailed the disadvantage that an attempt at enhancing the uniformity of the dopant and that of oxygen in solid solution results in disruption of an effort to preclude the occurrence of OSF.
An object of this invention, therefore, is to provide a novel single silicon crystal sparingly susceptible of the occurrence to stacking fault inducible by oxidation, and a method for the production of the single silicon crystal.
Another object of this invention is to fix conditions necessary for ensuring the uniformity of dopant and oxygen in solid solution and, at the same time, precluding the occurrence of OSF and to fix conditions for process control in commercial production of a CZ single silicon crystal fulfilling the requirement of uniformity by the Czochvalski method.